Fire control system for use on board a ship



Dec. 20, 1966 AKE H. P. BLOMQVIST FIRE CONTROL SYSTEM FOR USE ON BOARD A SHIP Filed June 22, 1964 I N VENTOR.

o AKE Huso PETRUS 5LOMQV/S7 BY A UM Clma United States The present invention relates to a fire control system for use on a moving carrier, particularly on board a ship, for laying a weapon on the ship for a target upon which fire is to be directed.

Such a fire control system comprises sighting or detecting means by which the direction and the range to the target can be measured, and a fire control computer, which from the data for the direction and range of the target from the sighting or detecting means and from other necessary data, such as the attitude, the speed and the course of the ship, the velocity and direction of the wind, the parallax, etc., computes the data necessary for the laying of the weapon on board the ship. The sighting or detecting means, which normally comprises a fire control radar, but which also can be of some other typefor instance, a laser sight-comprises a detector which can be directed at the target by rotation about at least one axis relative to the ship. If the tire control system is to be used for air targets, however, the detector must be rotatable about two preferably mutually orthogonal axes. In a fire control radar the detector comprises the antenna reflector of the radar station and consequently is rotatable about at least one axis relative to the ship, but in a fire control system for air targets it is rotatable about two mutually orthogonal axes.

In a fire control system of this type, it is generally desirable that the radar antenna, once it is directed upon the tar-get, will automatically follow the target so that the radar station will continuously supply the fire control computer with information regarding the range and direction of the target. Normally this is achieved by rotating the antenna reflector about each of its axes of rotation by means of a servomotor. The motor is controlled by a signal which is dependent on the deviation between the direction of the antenna reflector and the direction of the target. In a radar station, information about the deviation between the direction of the antenna reflector and the direction of the target is obtained by providing the radar station with lobe switching or a conically scanning antenna lobe, or with several simultaneously operating antenna lobes with somewhat deviating directions, whereby the radar station can determine the deviation between the direction of the antenna reflector and the direction of the target by comparing the amplitudes of the echoes received from the target in the different lobe directions. These echoes produce signals corresponding to this deviation for control of the servomotors rotating the antenna reflector about its two axes of rotation so that the servomotors try to direct the antenna reflector :at the target and thus eliminate the deviation. Several different devices in fire control radar stations for determining the deviation between the direction of the antenna reflector and the direction of the target are well known in the art, and therefore will not be described herein in detail.

By means of the above-described control of the servomotors rotating the antenna reflector, the antenna can in principle be brought to follow the target. In a fire control system of this type on board a ship, however, and particularly in a fire control system for air targets which are moving at very high velocities, it has been found to be practically impossible to obtain accurate and reliable atent Gr 3,293,643 Patented Dec. 20, 1966 ice target tracking in this simple way. The reason for this is the fact that, partly due to the movements of the ship, such as rolling, pitching and yawing, and partly due to the high velocity of movement of the target, the deviations between the direction of the antenna reflector and the direction of the target will be comparatively large and will vary rapidly in magnitude and in a direction requiring a high amplification in the above-described servomotor control circuits for the antenna reflector in order to cause the antenna reflector to follow the target accurately. The signal dependent on the deviation between the direction of the antenna reflector and the direction of the target, as received from the radar station and produced by lobe switching or in some other Way, cannot, however, be given a high amplification. Such signal comprises comparatively large noise components which would cause overdriving and thus create the risk that the antenna would lose the target; that is, that the target would be outside the lobe range of the antenna. If the signal is given a high amplification, the noise components may also cause overdriving of the amplifiers and the servomotors rotating the antenna. Furthermore, the wear on the servomotors and the mechanical rotating system will be increased.

One mode of solving this problem, at least partly, would be to mount the radar antenna on a gyro-stabilized platform so that the radar antenna would not participate in the movements of the ship, whereby these movements would not cause any deviations between the antenna direction and the direction of the target which would have to be eliminated by means of the antenna rotation sys tem. Such gyro-stabilizing of the antenna, however, is comparatively expensive and complicated.

A broad object of the present invention is to provide a fire control system of the type described above for use on board a ship, in which system the above-mentioned problems with respect to automatic target tracking by the detector, which is normally a radar antenna, are solved in a simple and reliable way.

According to the invention, this is achieved by controlling the servomotor system by which the detector is rotated about an axis relative to the ship, or about each of two mutually orthogonal axes in a fire control system for air targets, by means of three different signals. One of these signals is a signal received in the conventional manner from the detector means itself, and is dependent on the angular deviation about the axis of rotation of the detector associated with the servomotor system between the direction of the detector and the direction of the target. The second signal is received from a gyro responsive to angular velocity. The gyro is so mounted on the detector that the gyro is influenced by the angular velocity of the detector about the axis of rotation for the detector associated with the servomotor system and produces a signal proportional to this angular velocity. The third signal is obtained from the fire control computer, which is arranged according to the invention to compute the direction of movement and the velocity of the target and to produce a signal proportional to the angular velocity of the target, corresponding to the velocity and the direction of movement of the target, about the axis of rotation for the detector associated with the servomotor system. This third signal is connected to control the servomotor system so as to impart a corresponding angular velocity to the detector about said axis of rotation.

The signal from the angular-velocity-responsive gyro on the detector affects the servomotor system as a negative feedback, and will stabilize the detector so that its direction in space will not 'be affected by the movements of the ship. The signal received from the fire control computer which is proportional to the angular velocity of the targets about the axis of rotation of the detector will impart a movement to the detector such that the detector will automatically follow the target if the latter is moving at a constant speed on a straight course. The signal received from the detecting means, corresponding to the deviation between the direction of the detector and the direction of the target, need provide only such com paratively small and slow corrections of the direction of the detector as are necessary due to changes in the velocity and direction of the target, temporary external disturbances and inaccuracies in the control of the detector from the two other signals. Accordingly the signal received from the detecting means and dependent on the deviation between the direction of the detector and the direction of the target does not require large amplification. By means of the invention an accurate and reliable target tracking is achieved in a simple manner for large and rapid movements of the ship and for large target velocities also.

In the following pages the invention will be further described with reference to the accompanying drawing, which shows schematically, by way of example, a fire control system according to the invention, in which the sighting or detecting means consists of a fire control radar for air targets, said radar having an antenna reflector which can be directed in elevation about an axis parallel with the deck plane of the ship and in traverse about an axis parallel with the mast direction of the ship.

The exemplified fire control system comprises a conventional radar equipment R for transmitting radar pulses and receiving radar echoes which is connected to an antenna reflector 1 in the conventional manner, The antenna reflector 1 is mounted on one end of an arm 2, which is pivotable in a stand 3 about an axis H, which is assumed to be parallel with the deck plane of the ship. The stand 3 is mounted on a platform 4, which is journaled in the ship in such a way that it is rotatable about an axis S, which is perpendicular to the deck plane of the ship and thus to the axis H. The axis S is thu generally parallel with the [mast direction of the ship. Z is an imaginary axis perpendicular to the axis H as well as to the antenna direction designated A1 in the drawing. It should be noted that these axes S, H and Z are all imaginary geometrical spatial directions which are related to the ship and the antenna system so that the direction S is always parallel to the mast direction, the direction H is always parallel with the deck plane on the ship and perpendicular to the antenna direction A1 and the direction Z is always perpendicular to the antenna direction All as well as the direction H. The antenna arm 2 can be rotated about the axis H by means of a servomotor S1, whereas the platform 4 can be rotated about the axis S by a servomotor S2. Accordingly, the antenna reflector 1 can, by means of the two servomotors S1 and S2, be directed in traverse as Well as in elevation towards a target M. In the drawing the antenna direction is designated A1 and the true direction to the target M is designated A2. A signal generator 5 is coupled to the mechanical pivot shaft of the antenna arm 2 and produces a signal to the fire control computer 6 representing the angle H between the antenna direction A1 and the deck plane of the ship. A second signal generator 7 is coupled to the platform 4 for generating a signal to the fire control computer 6 representing the angle a in the deck plane of the ship between the projection of the antenna direction Al on the deck plane and a fixed direction in the deck plane of the ship. Thus the angle a indicates the traverse direction of the antenna relative to the ship, whereas the angle H indicates the elevation of the antenna relative to the ship and if the antenna is directed at the target M, these two angles will consequently define the direction of the target relative to the ship. The radar equipment R determines in a conventional manner the range of the target by measuring the difference in time between the transmitted radar pulses and the radar echoes received from the target, and conveys to the fire control computer 6 a signal representing this range L. By means of the data on the angles 0' and H and the range L supplied to the fire control computer 6 and other data regarding the attitude, the speed and the course of the ship, the velocity and direction of the wind, etc. supplied in the conventional way to the fire control computer but not specifically shown in the drawing, the fire control computer will in a conventional manner compute the necessary data for the laying of a weapon on the target M and will transfer these data in any suitable manner, not specifically shown in the drawing, to the laying system of the weapon.

The figure shows only those parts of the fire control system which according to the invention are of interest for the automatic tracking of the target M by the antenna 1 when the antenna has been directed close to the target in any suitable conventional way.

For such tracking the antenna reflector 1 and the radar equipment R are provided with means for lobe switching or a similar system so that the radar equipment R can measure the deviation between the antenna direction A1 and the true direction A2 to a target M. According to the invention the radar equipment R produces a first signal on the basis of the data regarding this deviation, which have been obtained by means of lobe switching or in any similar way. This signal is proportional to the angular deviation 6 about the axis Z between the antenna direction All and the direction A2 to the target M and is fed from the radar equipment A to a servomotor S2 through an adder amplifier 8. It is evident that 6 :8 cos H, where a is the angular deviation between the antenna direction Al and the target direction A2 as measured about the axis S in a projection on a plane parallel with the deck plane of the ship. The signal fed to the amplifier 8 from the radar equipment R is consequently proportional to 6 that is, to the angular deviation between the antenna direction A1 and the target direction A2 about the axis of rotation S for the platform 4 associated with the servomotor S2. The radar equipment further produces a second corresponding signal proportional to the angular deviation a about the axis H between the true target direction A2 and the antenna direction A1, and this second signal is supplied to a servomotor S1 through an adder amplifier 9. The two signals fed from the radar equipment R to the servomotors S1 and S2 and proportional to the angular deviations fi and 5 respectively, affect servomotors S1 and S2 in such a way that the servomotors try to rotate the antenna reflector 1 in a direction such that the angular deviations d and 6 are eliminated; that is, so that the antenna direction A1 coincides with the true direction A2 to the target M.

If the described automatic following control of the antenna had to neutralize the deviations between the antenna direction A1 and the direction A2 to the target M due to the rolling, pitching, and yawing movements of the ship and due to the movements of the target M, the signals from the radar equipment R proportional to B and 6 would have to be given a large amplification, which is undesirable in view of the fact that these signals comprise large noise components, as previously explained. To eliminate the need for such strong amplification, the system according to the invention comprises two conventional angular velocity-sensitive gyros G and G which, as schematically shown, are mounted on the antenna reflector 1 or any other member--for instance, the antenna arm 2, which moves together with the antenna reflector. Gyro G is so mounted that it measures the angular velocity of the antenna reflector 1 about the axis Z and generates a voltage proportional to this angular velocity dg/dt which is fed to the adder amplifier 8 and thus to the servomotor S2. As is apparent, the angular velocity tor about the axis S. The signal transmitted from gyro G to servomotor S2 for the platform 4 is consequently proportional to the angular velocity da/dl of the antenna reflector about the axis of rotation S associated with the servomotor S2. The second gyro G measures the angular velocity of the antenna reflector 1 about the axis H and supplies a signal proportional to this angular velocity dH/dt to the adder amplifier 9 and thus to servomotor S1. The angular velocities dg/dt and dH/dt respectively, measured by the two angular-velocity-sensitive gyros G and G reflect not only the rotational movements imparted to the antenna reflector 1 by the servomotors S1 and S2, but also the angular velocity components which are imparted to the antenna reflector about its two axes Z and H due to the rolling, pitching and yawing movements of the. ship. When the ship is yawing, for instance, a certain angular velocity is imparted to the antenna reflector 1 about its axis S, which angular velocity will affect the gyro G as described above. When the ship is pitching or rolling, a certain angular velocity is imparted to the antenna reflector about the axis H and is measured by the gyro 6 When the ship is pitching and rolling, the antenna reflector 1, provided that H is not zero, will also obtain a certain angular velocity about the axis Z, the magnitude of which is dependent on the angle between the antenna direction and the axis in the horizontal plane about which the ship is tilting, and the magnitude of the elevation angle H of the antenna. The signals proportional to the angular velocity dg/dt and dH/dt of the antenna reflector 1 received from the gyros G and G are fed to the servomotors S1 and S2 through the amplifiers 8 and 9 in a circuit such that they have the effect of negative feedbacks. The two negative feedbacks cooperate to drive the servomotors in such a way that the angular velocities of the antenna reflector about the axes H and Z become zero, whereby the direction A1 of the antenna reflector becomes stationary in space and independent of the movements of the ship, provided the amplification in the feedback loops may be regarded as infinite. These feedback loops may be readily given a high amplification whereby the antenna direction A1 is made independent of the movements of the ship with great accuracy.

As is conventional in a fire control system, the fire control computer 6 computes, on the basis of the supplied data, the velocity vector v of the target M; that is, the velocity and the direction of movement of the target. According to the invention the fire control computer 6 also computes the angular velocity of the target M about the axis Z in accordance with the direction of movement and the velocity of the target, and produces a signal proportional to this angular velocity a'gM/dt. This signal is fed from the fire control computer through the amplifier 8 to the servomotor S2. In this case also the magnitude dEZ'vI dull! dt (it where dM/dt is the angular velocity of the target about the axis S. The signal from the fire control computer 6 to the servomotor S2 is consequently proportional to the angular velocity of the target about the S axis of rotation associated with the servomotor S2. In a similar manner, the fire control computer 6 computes also the angular velocity of the target about the axis H and produces a signal proportional to this angular velocity dHM/dt. This signal is fed through the amplifier 9 to the servomotor S1. These two signals from fire control computer 6 control the servomotors S1 and S2 in such a way that the motors impart the same angular velocities dgM/dt and dHM/dt to the antenna reflector about the axes Z and H whereby the antenna 1 is automatically caused to follow the target M, if the same is moving with a constant velocity on a straight course.

By the combined control of the servomotors S1 and S2 according to the invention, as partly supplied by the cos H radar equipment in dependence on the angular deviation between the antenna direction A1 and the direction A2 to the target, partly by the angular-velocity-sensitive gyros G and G in dependence on the angular velocities of the antenna reflector 1 about the axes Z and H, and partly by the fire control computer 6 in dependence on the angular velocities of the target about these axes, an efiicient and reliable tracking of the target by the antenna 1 is obtained for very large and rapid movements of the ship and for high target velocities also.

As is obvious from the foregoing, all signals fed to the servomotor S2 for the platform 4 represent angles and angular velocities, respectively, about the axis Z, whereas the servomotor S2 rotates the platform and thus the antenna reflector about the axis S. Since, however, as mentioned before,

it is apparent that the servomotor S2 is capable of rotating the antenna reflector in such a way that the conditions 6Z=0 and n. is Tit dt are satisfied, if the amplification in the servo circuit may be regarded as infinite. Due to the component cos H in all signals, the amplification in the servo circuit comprising the servomotor S2 will vary with the magnitude of H. As a result, it may be suitable or necessary in some cases to pass the control signal for the servomotor S2 through an amplifier having the amplification factor l/cos H. Such amplifier is indicated by a block 10 and may consist for instance of an auto-transformer coupled to the pivot shaft of the antenna arm and having such a characteristic that the ratio between output voltage and input voltage is 1/ cos H.

It should be noted that the drawing shows a system according to the invention only schematically, and that the practical design of a system according to the invention may depart herefrom in several respects. For instance, the fire control computer 6 may be an electronic digital computer, in which case the signal generators 5 and 7 are preferably digital signal generators which convey the values of the angles a and H to the fire control computer 6 directly in digital form. The fire control computer 6 will then compute the quantities dM/dl and dHM/ d1 in digital form, and these digital values must be conveyed to digital-analog converters to be converted to analog signals which can control the servomotors S1 and S2. Furthermore, the invention may also be used in a fire control system for surface targets, in which case the radar antenna 1 is rotatable about only one axis, S.

While the invention has been described in detail with respect to a certain now preferred embodiment and example thereof, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made Without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. A fire control system for use on board of a ship, said system comprising, in combination, a sighting means for determining direction and range data of a target, said sighting means including a detector rotatable about a first axis substantially parallel to the deck plane of the ship and a second axis substantially normal thereto, first servomotor means rotating said detector about said first axis and second servomotor means rotating said detector about said second axis, said sighting means producing a first error signal corresponding to the angular deviation between the direction of said detector and the direction to the target about said first axis and a second error signal corresponding to the angular deviation between the direction of said detector and the direction to the target about a third axis perpendicular to the direction of the detector and said first axis of rotation of said detector; a first angular-velocitysensitive gyro means mounted on said detector so as to be responsive to the angular velocity of said detector about said first axis for producing a first rate signal proportional to said angular velocity and a second angular-velocity-sensitive gyro means mounted on said detector so as to be responsive to the angular velocity of said detector about said third axis for producing a second rate signal proportional to said angular velocity; a fire control computer for computing the velocity and the direction of movement of the target for aiming a Weapon on board the ship; circuit means feeding said direction and range data determined by said sighting means to said computer, said computer producing a first rate prediction signal proportional to the predicted angular velocity of the target about said first axis of rotation of said detector corresponding to said computed velocity and direction of movement of the target and a second rate prediction signal corresponding to the predicted angular velocity of the target about said third axis'corresponding to said computed velocity and direction of movement of the target; and means for feeding said first error signal, said first rate signal and said first rate prediction signal to said first servomotor means and for feeding said second error signal, said second rate signal and said second rate prediction signal to said second servomotor means.

2. A fire control system according to claim 1, comprising amplifying means having an amplification factor 1/ cos H, where H is the angle between the direction of said detector and the deck plane of the ship about said first axis of rotation of said detector, for amplifying the signal fed to said second servomotor means for rotating said detector about its second axis of rotation.

References Cited by the Examiner UNITED STATES PATENTS 7/1963 Goldberg 3437 3/1965 Harris 3437 

1. A FIRE CONTROL SYSTEM FOR USE ON BOARD OF A SHIP, SAID SYSTEM COMPRISING, IN COMBINATION, A SIGHTING MEANS FOR DETERMINING DIRECTION AND RANGE DATA OF A TARGET, SAID SIGHTING MEANS INCLUDING A DETECTOR ROTATABLE ABOUT A FIRST AXIS SUBSTANTIALLY PARALLEL TO THE DECK PLANE OF THE SHIP AND A SECOND AXIS SUBSTANTIALLY NORMAL THERETO, FIRST SERVOMOTOR MEANS ROTATING SAID DETECTOR ABOUT SAID FIRST AXIS AND SECOND SERVOMOTOR MEANS ROTATING SAID DETECTOR ABOUT SAID SECOND AXIS, SAID SIGHTING MEANS PRODUCING A FIRST ERROR SIGNAL CORRESPONDING TO THE ANGULAR DEVIATION BETWEEN THE DIRECTION OF SAID DETECTOR AND THE DIRECTION TO THE TARGET ABOUT SAID FIRST AXIS AND A SECOND ERROR SIGNAL CORRESPONDING TO THE ANGULAR DEVIATION BETWEEN THE DIRECTION OF SAID DETECTOR AND THE DIRECTION TO THE TARGET ABOUT A THIRD AXIS PERPENDICULAR TO THE DIRECTION OF THE DETECTOR AND SAID FIRST AXIS OF ROTATION OF SAID DETECTOR; A FIRS ANGULAR-VELOCITY-SENSITIVE GYRO MEANS MOUNTED ON SAID DETECTOR SO AS TO BE RESPONSIVE TO THE ANGULAR VELOCITY OF SAID DETECTOR ABOUT SAID FIRST AXIS FOR PRODUCING A FIRST RATE SIGNAL PROPORTIONAL TO SAID ANGULAR VELOCITY AND A SECOND ANGULAR-VELOCITY-SENSITIVE GYRO MEANS MOUNTED ON SAID DETECTOR SO AS TO BE RESPONSIVE TO THE ANGULAR VELOCITY OF SAID DETECTOR ABOUT SAID THIRD AXIS FOR PRODUCING A SECOND RATE SIGNAL PROPORTIONAL TO SAID ANGULAR VELOCITY; A FIRE CONTROL COMPUTER FOR COMPRISING THE VELOCITY AND THE 